In his first public appearance since his company's sluggish IPO, Facebook co-founder and CEO Mark Zuckerberg called the social network's stock performance "disappointing."

Facebook co-founder and CEO Mark Zuckerberg responded to questions during a session at the Tech Crunch Disrupt conference in San Francisco on Tuesday.

He also said that Facebook is pushing hard on mobile and will dive into search at some point, and he insisted that there are no plans for a phone. He said he can't emphasize it enough -- there will be no Facebook phone.

"The performance of the stock has obviously been disappointing," he said during an on-stage interview at the TechCrunch Disrupt conference in San Francisco late Tuesday afternoon. "How well we do with mobile is a big part of it.... A lot of stuff has changed. Six months ago, we hadn't launched our new apps, Apple hadn't announced their new iOS integration. People shouldn't underestimate how fundamentally good mobile is for us."

In the months running up to the company's IPO, there had been great expectations, with analysts and investors predicting that Facebook's stock would take off, soaring from its opening price of $38 a share to $50, $60 or even as high as $90.

Instead, the company's stock has been hammered, its price sinking instead of growing. On Tuesday, the company's share price closed the day at $19.43.

Appearing on the conference stage, Zuckerberg came across as calm and with a vision of where he wants to take his company. That vision is largely focused on mobile.

The move toward mobile may signal a shift from the pre-IPO days when there were doubts about Facebook's readiness to compete in the burgeoning mobile market. Facebook itself, in its pre-IPO filings with the U.S. Securities and Exchange Commission (SEC), listed mobile as one of its risk factors.

That's not how Zuckerberg sees it today.

"With the person using Facebook on mobile, there's more engagement and they're spending more time. Mobile users are more likely to be daily active users," he said. "Before, we had a mobile core team.... Now we are a mobile company."

Zuckerberg talked about the IPO issue for the first time since Facebook went public in May. He also stressed an emphasis on mobile for the company. And said engineers are working on search.

Dan Olds, an analyst at Gabriel Consulting Group, said Zuckerberg came across as being aware of the company's challenges and in control of figuring out one of those challenges -- mobile.